The nonequilibrium calculation for various neutral constituents in the mesosphere and lower thermosphere (Hunt, 1966) was extended by including the effects of molecular and eddy diffusion. Nitrogen and its oxides were added, and more recent laboratory data for chemical reaction coefficients were used. A special numerical technique has been developed to simultaneously solve time‐dependent continuity equations for 14 constituents. The preliminary result indicates that vertical eddy diffusion significantly reduces the irregular variations around 80 km and tends to lower the height of these irregular variations. However, the value of the eddy diffusion coefficient acceptable from the consideration of heat balance below ∼100 km cannot entirely smooth out these irregular distributions for atomic oxygen, ozone, and oxygen‐hydrogen compounds, although the smoothing effect for nitric oxide seems to be strong enough to eliminate the irregular variations above ∼70 km. The role of the transport terms for molecular and eddy diffusion in the continuity equation is illustrated explicitly and discussed for some representative cases. We show that the dynamic model fits the observational results for ozone and nitric oxide concentrations better than the static model and also offers a more adequate explanation for the observed diurnal variation in the OH airglow emission.

A method is described to accomplish automatic data selection and profile inversion to obtain ionospheric electron‐density profiles from digitized radio soundings. The profile inversion is based upon the well‐established formulation of Paul [1960] by which the optimum radio‐frequency sounding intervals can be specified from an approximate knowledge of the profile. The expected virtual height coordinates (h') at these frequencies (ƒ) are likewise estimated, and procedures are then used to select h'(ƒ) observations nearest the predicted coordinates from a subsequent digital ionogram. From these the next profile is obtained. The process adaptively follows the changing shape and detail of the profile. The procedure requires an average of 20 sec per profile on a standard data‐processing computer and can be adapted, with benefit to on‐line real‐time use in our ‘dynasonde,’ digital ionosonde.

Calculations have been made of the diurnal variations in minor neutral constituents in the mesosphere and lower thermosphere for the condition of 60 ø latitude, summer and winter, using the method developed by the authors [Shimazaki and Laird, 1970]. The excited molecular oxygen O•.(x/x•) has been added and the effects of absorption of Schumann-Runge bands have been taken into account. The results show significant seasonal differences, which may be interpreted mainly in terms of the difference of penetration of solar radiation and the duration of sunlit hours. However, the comparison of the observed seasonal and diurnal variations in the airglow emissions from hydroxyl, atomic oxygen (5577 A), and O•.(x/x•) with those calculated from models suggests that effects of large-scale meridional circulation (horizontal and vertical transports) may be important in explaining these observations. It is shown that the concentration of the constituents whose main loss mechanism is recombination with atomic oxygen decreases sharply above ~80 km. These constituents include OH, HO2, H•.Oe, and NO•. (nighttime) and the extension of this general theory may explain the sudden decrease observed by rockets in the water-cluster ion concentration above ~80 km. Ion-neutral chemistry should be important in explaining an observed increase in [NO] above •85 km.x Paper presented at COSPAR Symposium on D-and E-Region profiles and diurnal variations of the different constituents. Moreover, the model was not appropriate for extensive comparison with observations, because most rocket and satellite observations have been made at middle or high latitudes and at seasons other than equinoxes.To obtain a better understanding of the effects of photodissociation, chemical reactions, and dynamical (eddy diffusion) processes, and also to make more realistic comparisons, we have made model calculations for the latitude of 60 ø for summer and winter. It is well known that the mesophere is much warmer in winter than in summer, whereas the temperature in the thermosphere and stratosphere is greater in summer than in winter. Corresponding to this difference in the temperature structure, summer and winter should have different density variations with height, affecting the absorption of solar radiation energy. The chemical reaction coefficients for some reactions are sensitive to temperature changes, and the upper atmosphere is known to be more turbulent in winter than in summer. Thus, examination 24 SHIMAZAKI AND LAIRD of the difference between the summer and winter models could be useful in identifying the effects of photodissociation, chemical reactions, and eddy diffusion. There are major North American missile ranges at Ft. Churchill (59øN), Wallops Island (38øN), White Sands (32øN), and Eglin (30øN) from which rockets making observations that can be compared with our model have been or could be flown. Our calculations should be directly comparable to rocket observations made at Ft. Churchill and should be comparable, after suitable allowance for probable...

Martyn [1947] suggested that e!ectromag-neticaFy driven drift motions cause much of the variations of the ionospheric F2 layer during magnetic storms. In spite of the considerable success of this theory [Maeda and Sato, 1959], the cause of the variations during storms is still not clear [Reid, 1967; Rishbeth and Garriott, 1969]. There are two reasons for this uncertainty. First, the electric fields in the region have not yet been measured simultaneously with storm-re!areal F•-]ayer variations.

Exceptionally high ozone ground level concentrations (>200 ppb) observed in Denver, Colorado, on the afternoon of March 4, 1978, are explained in terms of enhanced photochemistry combined with isentropic transport of ozone from the stratosphere. The maximum ozone concentrations observed on March 4 is the highest recorded for the 1975-1978 period. Inspection of the local pollutant and meteorological data shows high early morning accumulation of precursor gases and enhanced potential for afternoon photochemical activity. Objective cross-sectional analysis and trajectories on isentropic surfaces indicate that some air parcels that mixed into the boundary layer over the city on the afternoon of March 4 were derived from a stratospheric intrusion 3 days earlier. It is concluded that a combination of these factors resulted in the exceptionally high ozone concentrations.